An arc flash study calculates how much energy would be released if an arc fault occurred at each piece of electrical equipment, and how far from it a person could be burned. The results go on labels fixed to the equipment and into your electrical safety program, so qualified workers know the hazard before they open a cover. We carry out studies to CSA Z462 using recognised calculation methods, and recommend practical ways to bring high hazard levels down.
An arc flash is an explosive release of heat, light, pressure and molten metal when current flows through the air between conductors. It can happen when a tool slips, a connection fails or a breaker is racked in on a fault. The injuries are severe and the events are fast. CSA Z462, the Canadian standard for workplace electrical safety, expects employers to assess this risk before anyone works on or near energized equipment, and an incident energy study is the most common way to do that for building and industrial systems.
A study does not make energized work safe. The safest choice is almost always to de-energize and lock out the equipment. The study and labels support that program and tell qualified workers what protection is needed when energized work is justified. Untrained people should never open energized electrical equipment.
What we look at
- Every piece of equipment likely to be examined, adjusted or serviced while energized: switchgear, switchboards, panelboards, MCCs, disconnects, transformers and control panels.
- Available fault current from the utility and other sources such as generators and large motors.
- Protective device types and settings, which determine how long an arc lasts.
- Equipment construction: enclosure size, conductor gap and configuration, which affect how the arc behaves.
- Working distances for the tasks typically done on each piece of equipment.
- Existing labels, your electrical safety procedures and the PPE your workers have.
How the study gets to a label
An arc flash study is built on a short-circuit and coordination model of the system. The fault current at each bus tells you how big the arc could be; the upstream protective device's time-current curve tells you how long it would last. Those, together with the equipment's construction and the working distance, give the incident energy, which is the heat a worker's face and chest would receive.
The single biggest lever is usually clearing time. A fault that is cleared in a fraction of a second releases far less energy than one that lasts a second or more, which is why the same panel can have very different results depending on how the breaker above it is set.
How it works
- Brief. We start by asking why: a new safety program, an insurer or auditor request, a labelling gap, an incident or a system change. We agree which equipment is in scope.
- Field data collection. We walk the system and record nameplates, protective devices and settings, cable sizes and lengths, and equipment types. Opening covers is done by qualified workers under your procedures, and some data is best gathered during a planned shutdown.
- Modelling and calculation. We build the short-circuit and coordination model, calculate incident energy and arc flash boundaries using recognised methods such as IEEE 1584, and check results against the equipment's ratings.
- Mitigation review. Where results are high, we look for practical reductions, such as changed settings, a maintenance switch, remote racking or operation, or equipment changes.
- Labels and report. We produce labels for each piece of equipment and a report explaining the results. Labels can be installed by your staff or electrical contractor, and we can verify placement.
What to have ready
- Single-line diagrams, panel schedules and any previous short-circuit, coordination or arc flash study.
- Your electrical safety procedures and the arc-rated PPE your workers currently use.
- Maintenance and test records for breakers and relays, since a poorly maintained breaker may clear more slowly than its curve says.
- Windows when planned shutdowns are possible, and a qualified contact for opening equipment.
What you get
- A label for each piece of equipment showing the information CSA Z462 calls for, such as nominal voltage, arc flash boundary, incident energy at the working distance and shock approach boundaries.
- A report listing the results for each piece of equipment and the assumptions behind them.
- Equipment with high incident energy flagged, and recommended ways to reduce it.
- Any equipment found under-rated for the available fault current.
- An updated single-line diagram and a system model that can be updated when things change.
Labels are only as good as the model behind them. If settings are changed, a transformer is replaced or the utility upgrades its service, the numbers can go up or down. CSA Z462 expects the assessment to be reviewed when the system changes and at regular intervals, commonly no more than five years. Check the current edition for the exact requirement.
Who it's for
- Employers with maintenance staff or contractors who work in electrical rooms.
- Safety managers building or auditing an electrical safety program.
- Facility managers whose equipment has no labels, or labels that predate major changes.
- Industrial and institutional sites with large services, MCCs and switchgear.
For background, read arc flash basics, reading an arc flash label, what happens in an arc flash study and lockout and tagout.
Common questions
Can we use PPE category tables instead of a study?
CSA Z462 allows a table method for some equipment within set limits, but the limits are easy to exceed in practice and the tables cannot tell you where a hazard is unusually high. Many employers use an incident energy study so every label reflects the actual system.
Do you train our workers?
We explain the results and how to read the labels. Electrical safety training for qualified workers should come from a recognised provider, and our report can be used as part of that training.
Why do some small panels have higher results than the main switchboard?
Because incident energy depends heavily on how long the arc lasts. A small panel fed from a large breaker with a slow setting can see a long-lasting arc, while the main switchgear may be protected by a faster device.